Electrical connector having a contact spring mounted in a housing cavity

ABSTRACT

An electrical connector, of the type having a contact spring for unilaterally clamping a conductive contact member and being mounted within the cavity formed in a housing having a guide aperture intersecting the cavity and defining an insertion axis along which the contact member may be inserted for engagement with the contact spring, is characterized by the contact spring comprising an elastic contact portion normally biased toward the insertion axis for contacting an inserted conductor member with a predetermined unilateral contact force and a resilient portion attached to the contact portion and having a free end normally held in a deflected position by engagement with abutment means for outwardly biasing the contact to present an initial plugging force approaching zero and being deflectable to a position out of contact with the projection for presenting a sharply increasing plugging force and a gradually increasing contact force.

United States Patent Wessely [72] inventor:

[73] Assignee:

Hermann Wessely, Munich, Germany Siemens Aktiengesellschaft, Berlin andMunich, Germany [221 Filed: Sept. 25, 1969 211 Appl.No.: 861,022

[30] Foreign Application Priority Date Sept. 26, 1968 Germany ..P 17 90199.4

[52] US. Cl. ..339/65, 339/210 R, 339/258 R [51] Int. Cl ..H0lr 13/62[58] Field of Search ..339/65, 66, 176, 210, 217, 339/258 [56]References Cited UNITED STATES PATENTS 3,464,054 8/1969 Mansfield ..339/176 MP 2,875,425 2/l959 Gilbert ..339/176 MP [451 Feb."'29, 1972 PrimaryExaminer.loseph H. McGlynn AttorneyHill, Sherman, Meroni, Gross &Simpson 571 ABSTRACT An electrical connector, of the type having acontact spring for unilaterally clamping a conductive contact member andbeing mounted within the cavity formed in a housing having a guideaperture intersecting the cavity and defining an insertion axis alongwhich the contact member may be inserted for engagement with the contactspring, is characterized by the contact spring comprising an elasticcontact portion normally biased toward the insertion axis for contactingan inserted conductor member with a predetermined unilateral contactforce and a resilient portion attached to the contact portion and havinga free end normally held in a deflected position by engagement withabutment means for outwardly biasing the contact to present an initialplugging force approaching zero and being deflectable to a position outof contact with the projection for presenting a sharply increasingplugging force and a gradually increasing contact force.

4 Claims, 11 Drawing Figures I 22 r a Z6 PAIENTEnrms 1972 3,646,500

SHEET 1 [IF 4 BY xii/Z4, W 522mm;

ATTORNEYS PAIENTEDFEBPS 1972 3. 645,500

SHEET u [1F 4 INV OR //2MAA/A/ 5550/ ATTORNEYS ELECTRICAL CONNECTORHAVING A CONTACT SPRING MOUNTED IN A HOUSING CAVITY BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention generallyrelates to electrical connectors and more particularly refers to anelectrical connector of the type having a contact spring mounted in ahousing cavity for plugging engagement with a conductive contact memberto provide an electric connection.

2. Description of the Prior Art Major electronic equipment and systems,particularly solid state circuit devices such as data processingequipment generally comprise individual pluggable building components orsubcircuits to facilitate production and servicing. In order to make aplug connection, a pluggable, conductive contact member, for example aspring bar, is electrically connected to each circuit component orsubcircuit, or the conductor panels include integral conductor tracks orcircuits extending to a peripheral edge of the circuit panel so that theconductor panel is directly pluggable into a correspondingly designedreceptacle to form an appropriate electric connection or circuit.

The ever-increasing miniaturization of almost all electrical andmechanical circuit components, and particularly the everincreasing useof integrated circuitry, requires corresponding miniaturization of plugcontact members and contact springs for receiving the contact members.For example, it is becoming common practice to allocate across-sectional area in the order of 5X5 mm. for contact points orcontact members, thereby providing only a few millimeters in which todimension a contact spring and the insulative wall thickness forming ahousing for receiving the contact spring.

To assure perfect operation, a contact spring must fit snugly within ahousing cavity to prevent the spring from being pushed rearwardly duringinsertion of the contact member, and the contact spring also must havesufficient clearance in the spring cavity or chamber to prevent thecontact member from scrapping, hooking or impacting on the cavity orchamber walls.

In order to form a safe electrical connection, the unilateral contactforce between the contact spring and the contact member must notdecrease below a minimum value, and on the other hand, the contact forcemay not exceed a maximum value that will cause abrasion of the contactcoating, which may, for example be gold. Further, to assure asubstantially consistent contact force, the contact spring should have aminimum elastic force fluctuation due to manufacturing tolerances whichmay occur in both the contact spring and the contact members.

Miniaturization of circuit components has also resulted in an increasein the number of contact members disposed on a circuit board forsimultaneous plugging into a receptacle having a plurality of contactsprings. Thus, unless the plugging force, i.e., the resistance toinsertion of the contact member into the contact spring, is maintainedat a minimum, the accumulated plugging forces of a plurality of contactsprings to be simultaneously plugged may exceed the mechanical strengthof the circuit plates.

It should be noted that the requirements of a minimum plugging force anda sufficiently high contact force substantially independent ofmanufacturing tolerances in the production of the contact elements arecontradictory. In particular, a minimum plugging force and asufficiently high contact force requires that the spring force increaserapidly in response to increased opening or deflection of the spring asthe contact member is inserted, thereby requiring a spring deflectioncurve, i.e., a graphical representation describing the force exerted bythe contact spring as a function of spring deflection, to be steeplysloped. On the other hand, the requirement of a contact forcesubstantially independent of manufacturing variations in the thicknessof the contact member requires a spring deflection curve that issubstantially flat.

One prior art contact spring of which I am aware achieves a compromisebetween the contradictory requirements by providing a spring having adeflection curve with an initial steeply sloped portion changing to asubstantially flat portion. That prior art spring has a lug orprojection bent outwardly at an angle of approximately and having an endportion bearing down against a wall of the spring housing. As thecontact member is inserted, the point of support of the spring endshifts, due to deformation of the spring, toward a base wall of thecavity, thereby to increase the spring lever arm. To shift the point ofadhesion of that prior art spring on the chamber wall requiresovercoming a frictional force which may increase the plugging force.Further, if the chamber wall is somewhat roughened by frequent pluggingor by dust particles, the shifting of the projection along the chamberwall may be severely impeded, thereby increasing the plugging force inan unacceptable manner. That spring also requires substantial space in adirection perpendicular to the longitudinal extension of a multicontactspring bar, thereby limiting its use in a spring bar having a pluralityof closely spaced rows of contacts.

SUMMARY OF THE INVENTION In accordance with the principles of thepresent invention, a contact spring for unilaterally clamping a contactmember and being mounted in a cavity of a housing having a guideaperture intersecting the cavity and defining an insertion axis alongwhich a contact member may be inserted for engagement with the spring ischaracterized as comprising an elastic contact portion biased toward theinsertion axis and an elastic leg portion attached to the contactportion and having a portion thereof held in a deflected position priorto a contact member being inserted, by engagement with abutment meansand being deflectable out of contact with the projection as the contactmember approaches a fully inserted position, thereby to elasticallysupport the spring contact portion in a manner to provide a pluggingforce initially approaching zero and sharply increasing to the desiredcontact force as the contact member is inserted into the contact spring.The elastic support provides a gradually increasing contact forcesubsequent to the deflected portion lifting out of contact with theabutment means, thereby to reduce any effect manufacturing tolerancesmay have on the unilateral contact force.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. la is an isometric view of oneembodiment of an unmounted contact spring embodying the features of thepresent invention;

FIG. lb is a side elevational view of the contact spring shown in FIG.la and illustrating a spring housing in cross section;

FIG. 2 is a graph illustrating a deflection curve of the contact springshown in FIGS. Ia and lb with the abscissa representing deflection ofthe spring by insertion of a contact member and the ordinaterepresenting the unilateral force between the contact spring and thecontact member.

FIG. 8 is a schematic view illustrating basic elements of the contactspring to facilitate understanding of the principles of the presentinvention;

FIG. 4 is a graph illustrating variations in plugging force as afunction of the depth of insertion of the contact member with theabscissa representing the inserted depth and the ordinate representingthe plugging force;

FIGS. 5, 6 and 7 are isometric views illustrating alternativeembodiments of contact springs constructed in accordance with theprinciples of the present invention;

FIG. 8a is a fragmentary transverse sectional view similar to FIG. lband illustrating a further alternative embodiment of the presentinvention;

FIG. 8b is a fragmentary end elevational view of the contact springillustrated in FIG. 8a with the housing shown in cross section; and

IOI025' 0763 FIG. 9 is a fragmentary side elevational view of a stillfurther embodiment of the present invention.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS Referring to thedrawings, and first particularly referring to FIGS. 10 and lb, a contactspring 10, constructed in accordance with the principles of the presentinvention, comprises a U-shaped member composed of an elastic,conductive material, for example sheet copper, and having a pair ofgenerally upstanding elastic leg portions 11 and 12 connected by a baseportion 13.

A sheet-form mounting plate 14 characterized by an offset connecting lug15 is secured to the spring base 13 by spotwelding or other suitablesecurement means and is clamped in a recess 16 formed between matinghousing parts 17 and 18 composed of insulating material, thereby tosecurely support the contact spring within the housing. The connectinglug 15 extends beyond the housing parts 17 and 18 to facilitateconnecting a lead thereto. With the mounting plate 14 securely clampedbetween the housing parts 17 and 18 and the spring base 13 securelyfastened to the mounting plate, the pair of upstanding elastic legportions 11 and 12 form mechanically independent leaf springs eachhaving one end portion firmly clamped to the housing.

It is contemplated by one embodiment of the present invention to formelastic contact portions or tabs by shearing rectangular tabs as at 20and 21 along three sides from an upper portion of the legs 11 and 12 sothat the tabs are integrally attached along a fourth side of therectangle to the leg portions along planes substantially midway betweenthe fixed lower end portions of the legs and free upper end portions asat 22 and 23. Each of the contact tabs 20 and 21 have first portions asat 23 and 24 bent inwardly of the U-shaped contact spring 10 andconverging toward each other and second or upper portions as at 26 and27 diverging away from each other to form a mouth or entrance forreceiving a contact member (not shown).

With the contact tabs 20 and 21 punched from the upstanding spring legs11 and 12, upper portions of each leg have a parallel pair of narrowstrips as at 28 and 29 interconnected at the upper free ends by atransversely extending bridge portion as at 31.

The upper housing part 17 has a guide aperture 32 formed therein anddefining an insertion axis 33 contained within a juncture plane passingbetween the contact tabs 20 and 21 and along which the contact membermay be inserted for deflection of and engagement with the contact springfor completing an electric connection. The guide aperture 32 intersectsa spring cavity 34 receiving the contact spring 10 and defined by thehousing parts 17 and 18.

In accordance with the principles of the present invention, the upperfree ends 22 and 23 of the spring legs ll and 12 are deflected outwardlyand held in the deflected position by abutting engagement with abutmentmeans including a pair of projections 36 and 37 extending inwardly ofthe cavity 34 and oppositely disposed at peripheral edge portions of theinsertion aperture 32, thereby to initially outwardly bias the con tacttabs 20 and 21 so that curved portions of the tabs bearly contact eachother along the juncture plane containing the insertion axis 33 and thuspresenting an initial resistance to in sertion of the contact member, orplugging force, approaching zero.

Further, by disposing the projections 36 and 37 on opposite peripheraledge portions of the insertion axis 32, those projections form centeringbridges for guiding the contact member along the insertion axis 33 andfor centering the opposed contact tabs 20 and 21, thereby to preventloose plugging even when the contact member is initially inserted at anangle eschewed relative to the insertion axis. Thus, the contact spring10 and housing parts 17 and 18 form a so-called headcentering contactspring. It should also be noted that by disposing the centeringprojections 36 and 37 parallel to the insertion axis, those projectionsmay be sufficiently long to provide a large overlapping of the springlegs 11 and 12, since the contact is not dimensionally restricted inthat direction.

From the foregoing description, it should be noted that the contactspring 10 of the present invention includes elastic contact tabs 20 and21 separately supported on the elastic spring legs 11 and 12, which inturn are normally held in a deflected position by abutting engagementwith the projections 36 and 37 in a manner to outwardly bias the contacttabs for providing an initial plugging force approaching zero. As thecontact member is inserted central portions of the spring legs Hand 12intermediate the clamped and free ends thereof are out wardly deflecteduntil the spring legs lift away from the projections 36 and 37 whichoccurs as the contact member approaches a fully inserted position. Asillustrated graphically in FIG. 2, the deflection curve of each of theelastic leg portions 11 or 12 has a sharply increasing portion as at adue to a decreasing biasing force counteracting the unilateral contactforce between the contact portions 20 and 21 and the contact member.

To facilitate description of the theoretical aspects of the presentinvention, one of the spring legs 11 or 12 of the contact spring 10 isschematically shown in FIG. 3 and identified by the reference characterF. The elastic leg portion of leaf spring F has one end portion Eunilaterally clamped to represent the lower end of the spring legs andhas a free end portion thereof deflected and held in the deflectedposition by abutment with the projection or support Z. Due to thedeflection of the elastic spring F, the support Z exerts a biasing forceon the free end of the spring as represented by the force vector V,thereby to produce a torque Me on the spring F at the clamped endportion E.

If a contact force P due to insertion of a contact member acts on thecontact point K intermediate the clamped end E and the free end, thespring F deflects in the direction of the force vector P, and thus thebending or arcuate deflection of the spring F decreases tocorrespondingly decrease the bias force V. Since the sum of thedeflection force F and the biasing force V counteract the torque Mecreated on the spring at the clamped end portion E, as the biasing forceV decreases due to deflection or straightening of the elastic spring F,the deflecting force P must correspondingly increase to further deflectthe spring. When the free end of the spring F moves out of contact withthe support Z, the biasing force P necessary for further deflection ofthe contact point K is only dependent upon the properties of the springportion between the clamped end portion E and the contact point K. Thus,the deflecting force required for deflection after the free end liftsout of contact with the projection increases at a considerably lesserrate than when the free end is in contact with the projection, asrepresented by the upper portion B of the deflection curve asillustrated in FIG. 2.

A contact M is superimposed on the graphical representation of thedeflection curve with dashed lines separated by the distance Arepresenting minimum and maximum widths of the contact member due tomanufacturing tolerances. The steeply sloped portion A of the deflectioncurve represents the rapid increase in the deflection force F while thefree end of the spring is in contact with the abutment 2, whereas thesubstantially flatter portion B of the curve represents the increase inthe deflection force subsequent to the free end moving out of contactwith the projection, which occurs at a deflection of f The deflection fcorresponds to one-half of the minimum thickness of the contact member Mtaking into consideration manufacturing tolerances of the contact memberand the contact spring, thereby positioning any variation in thedeflection force P, or in the contact force between the contact memberand the contact spring, in the substantially flat portion B of thedeflection curve, and thus minimizing variations on the contact forcedue the manufacturing tolerances. Further, to achieve a minimum pluggingforce it is desirable to dimension the contact spring and theprojections so that the tolerance range begins at the deflection f PointC on the graph represents the intersection of the flatter portion B ofthe curve with the insertion axis 33, or a longitudinal axis of thecontact member M, and the ordinate of the point C would be the initialforce necessary to deflect the spring F, or initial plugging force,which would occur if the free end of the spring was not initiallydeflected and held in the deflected position by abutting engagement withthe projection Z.

Differences in the required plugging force for an elastically centeredcontact spring, constructed in accordance with the principles of thepresent invention, and a similarly configured, nonelastically centeredspring are graphically represented in FIG. 4. That graph illustrates thecalculated course of the plugging force S as a function of the pluggingpath W or extent of the insertion of the contact member into the contactspring. The solid line curve a represents the plugging force for anelastically centered spring, whereas the dashed line b represents anoncentered spring. In the calculations, it was assumed that the contactpoint had an arcuate configuration and that the contact member wassquared off perpendicularly to a longitudinal axis thereof. In practice,the contact members generally have a slightly beveled free end portion.

The plugging force for an elastically centered contact spring, asrepresented by the curve a, steadily increases from zero to a maximumvalue and then decreases to a constant value necessary for overcomingsliding friction between the contact member and the contact spring. Fora nonelastically centered contact spring, the initial plugging force hasa value substantially exceeding the maximum value for an elasticallycentered spring, and the plugging force steeply decreases untilovercoming the adhesive friction and then gradually decreases to theconstant terminal value necessary for overcoming the sliding friction.

Utilizing contact springs providing a contact force of 145 i 5 p andmounted in a 24-pole spring bar housing, the following values weremeasured for the plugging force and the traction force:

Type of Spring Plugging Force Traction Force From the table, it shouldbe noted that the plugging force for a nonelastically centered contactspring is approximately 40 percent higher than the plugging force of anelastically cen tered contact spring, constructed in accordance with theprin ciples of the present invention.

As illustrated in FIGS. 5 through 7, inclusive, contact springsconstructed in accordance with the principles of the present inventionmay have various alternative configurations, and structural elements ofthe alternative embodiments having a similar configuration to thoseshown in FIGS. la and 1b are identified with like reference charactersto which a small letter a, b or c has been added.

In the embodiment of the contact spring a, as illustrated in FIG. 5, twopairs of contact tabs as at a, 20a and 21a, 21a are respectively punchedfrom opposite, lateral side edge portions of the spring legs 11a and120. That embodiment is particularly appropriate for planar contactmembers as opposed to arcuately shaped contact members. As illustratedin FIG. 6, the contact tabs 20]: and 21b are attached at an upper endportion thereof to the spring legs 11b and 12b, thereby to furtherlessen any possibility of damage to the contact tabs by an end portionof the contact member abutting the free end of the tabs.

It is also contemplated by the present invention, as illustrated in FIG.7, to form the contact tabs 20c and 210 from sheet material independentof the spring legs 11c and 12c and attach the contact tabs to the springlegs by welding or other suitable securement means. Although thelast-mentioned embodiment requires a somewhat more expensivemanufacturing operation, that embodiment permits an optimum selection ofmaterials for the contact tabs and the spring legs.

Referring now to FIGS. 3a, db and 9, it is also contemplated by thepresent invention to provide a contact spring of the socalled laterallycentered type, as generally indicated at 40, wherein projections 41 forholding portions of the spring in a deflected position prior toinsertion of the contact member are disposed along opposite sidewalls asat 42 of the spring cavity 43 defined by the housing 44 for guiding sideedge portions of the contact member disposed laterally of the contactspring.

The contact spring 40 is a generally U-shaped sheet-form member composedof an elastic, conductive material and having a mounting plate includinga connecting lug secured to a medial or base portion (not shown) of theUshaped member. Upstanding spring leg portions 46 and 47 of the contactspring 40 each have a pair of centering tabs as at 48 punched outwardlytherefrom at laterally opposite side portions and attached along anupper edge to form integral tabs. Associated pairs of the centering tabs48 disposed on similar lateral sides of the contact spring 40 convergeinwardly of the U-shaped contact spring and toward an insertion axis 49defined by the guide aperture 51 formed in the housing 44 andintersecting the spring cavity 43. Contact portions or tabs 52 areformed by bending a central portion of the spring legs 46 and 47intermediate the pair of centering tabs 48 into a tuliplikeconfiguration. With the contact spring 40 properly mounted in the cavity43 so that lower free end portions of the centering tabs 48 areoutwardly deflected by abutting engagement with opposite side edges asat 53 of the projections 41, the contact portions 52 are outwardlybiased to provide an initial plugging force approaching zero. Theoutward bias provided by the centering tabs 48 decreases the deflectionforce otherwise necessary to spread the contact tabs 52 as the contactmember is inserted. Just prior to the contact tabs 52 being spread asufficient distance to permit full insertion of the contact member, thecentering tabs are deflected out of engagement with the projections 41,thereby to render further increases in the deflection force andcorresponding contact force dependent solely upon the elasticcharacteristics of the spring legs 46 and 47. In that manner, adeflection curve similar to that shown in FIG. 2 is provided for anelastically, laterally centered contact spring.

A still further embodiment of the present invention, as illustrated inFIG. 9, contemplates eliminating the necessity for centering projectionssimilar to the projections 41 by initially bending the lateral centeringtabs 48a past the insertion axis 490 so that in the rest position,without the contact member being inserted, opposed ones of the centeringtabs 48a engage along a juncture plane containing the insertion axis. Inthat manner, the contact portions or tabs 52a are outwardly biased bycoaction between the opposed centering tabs 48a, thereby to provide asharply increasing plugging force until the centering tabs are deflectedout of contact, at which time the deflection force or contact forcegradually increases with further deflection of the contact tabs.

It should also be noted, that contact springs constructed in accordancewith the principles of the present invention need not have asubstantially U-shaped configuration, but may comprise a single leafspring anchored at a lower end portion to a spring housing. A contactspring of that configuration has particular utility in plug connectorsfor direct plugging of printed circuit panels. Also, by disposing a pairof independently mounted leaf spring on opposite sides of an insertionaxis and electrically insulating the pair of springs, a bilaterallyprinted circuit board may be directly plugged in a manner to formseparate electric connections on opposite side surfaces of the panel.

Although those versed in the art may suggest various minormodifications, it should be understood that I wish to embody within thescope of the patent warranted hereon all such modifications asreasonably and properly come within the scope of my contribution to theart.

I claim as my invention:

1. An electrical connector for receiving a contact member comprising:

means forming a housing having a cavity formed therein and a guideaperture intersecting the cavity and defining an insertion axis alongwhich a contact member may be inserted; a generally U-shaped contactspring having a medial base portion clamped to a cavity wall portiondisposed opposite said guide aperture and a pair of generally upstandingelastic leg portions disposed on opposite sides of the insertion axis,elastic contact portions disposed on said pair of elastic leg portionsand converging toward the insertion axis for engagement by the contactmember to form an electric connection,

said contact portions including substantially rectangular tabs punchedalong three sides from said elastic leg portions and being inwardly bentalong a fourth side;

abutment means attached to said housing means and extending inwardly ofsaid cavity,

said abutment means having a pair of oppositely disposed projectionsattached at peripheral edge portions of said guide aperture for guidingthe contact member.

upper free end portions of said elastic leg portions being outwardlydeflected and engaging side surfaces of said projections disposedoppositely of said guide aperture for outwardly biasing said contactportions in a manner to provide a minimum resistance to insertion of thecontact member, and

said upper free end portions of said elastic leg portions beingdeflected out of engagement with said abutment means as the contactmember approaches a fully inserted position,

thereby to provide a contact spring presenting a sharply increasingplugging force until the contact member approaches the fully insertedposition and presenting a gradually increasing contact force subsequentto said upper free end portions moving out of engagement with saidabutment means.

2. In an electric contact device having a contact spring mounted on oneof its sides in a spring housing in a manner to form a detachableelectric contact engageable with a contact pin which determines aninsertion axis, the improvement comprising said contact spring beingdivided into at least two parts which extend substantially inlongitudinal directions of said contact spring, one of said parts beingbent toward the insertion axis, and the other of said parts beingsupported by means forming a support in a manner so that thelast-mentioned one of said parts is only lifted from said support meanswhenever the contact pin is partially inserted into the contact device,said first mentioned part including a substantially rectangular tabpunched along three sides from said contact spring and being bent towardthe insertion axis along a side of said tab.

3. An electric contact device as defined in claim 2 and furthercharacterized by said rectangular tab being bent toward the insertionaxis along a side of said tab furthest from the point of insertion ofthe contact pin.

4. An electric contact device as defined in claim 2 and furthercharacterized by said rectangular tab being bent toward the insertionaxis along a side of said tab nearest the point of insertion of thecontact pin.

1. An electrical connector for receiving a contact member comprising:means forming a housing having a cavity formed therein and a guideaperture intersecting the cavity and defining an insertion axis alongwhich a contact member may be inserted; a generally U-shaped contactspring having a medial base portion clamped to a cavity wall portiondisposed opposite said guide aperture and a pair of generally upstandingelastic leg portions disposed on opposite sides of the insertion axis,elastic contact portions disposed on said pair of elastic leg portionsand converging toward the insertion axis for engagement by the contactmember to form an electric connection, said contact portions includingsubstantially rectangular tabs punched along three sides from saidelastic leg portions and being inwardly bent along a fourth side;abutment means attached to said housing means and extending inwardly ofsaid cavity, said abutment means having a pair of oppositely disposedprojections attached at peripheral edge portions of said guide aperturefor guiding the contact member, upper free end portions of said elasticleg portions being outwardly deflected and engaging side surfaces ofsaid projections disposed oppositely of said guide aperture foroutwardly biasing said contact portions in a manner to provide a minimumresistance to insertion of the contact member, and said upper free endportions of said elastic leg portions being deflectEd out of engagementwith said abutment means as the contact member approaches a fullyinserted position, thereby to provide a contact spring presenting asharply increasing plugging force until the contact member approachesthe fully inserted position and presenting a gradually increasingcontact force subsequent to said upper free end portions moving out ofengagement with said abutment means.
 2. In an electric contact devicehaving a contact spring mounted on one of its sides in a spring housingin a manner to form a detachable electric contact engageable with acontact pin which determines an insertion axis, the improvementcomprising said contact spring being divided into at least two partswhich extend substantially in longitudinal directions of said contactspring, one of said parts being bent toward the insertion axis, and theother of said parts being supported by means forming a support in amanner so that the last-mentioned one of said parts is only lifted fromsaid support means whenever the contact pin is partially inserted intothe contact device, said first mentioned part including a substantiallyrectangular tab punched along three sides from said contact spring andbeing bent toward the insertion axis along a side of said tab.
 3. Anelectric contact device as defined in claim 2 and further characterizedby said rectangular tab being bent toward the insertion axis along aside of said tab furthest from the point of insertion of the contactpin.
 4. An electric contact device as defined in claim 2 and furthercharacterized by said rectangular tab being bent toward the insertionaxis along a side of said tab nearest the point of insertion of thecontact pin.